Prior art workers have devised various embodiments of sewer cleaning machines of the type comprising an elongated cable provided at its forward end with a sewer cleaning tool. The cable is caused to rotate, which in turn imparts rotation to the cleaning tool. Rotation of the cable and cleaning tool in the forward direction, will cause them to advance through the sewer pipe being cleaned. When an obstruction is reached, the cleaning tool will remove the obstruction by a cutting action.
A typical prior art sewer cleaning machine is provided with a prime mover usually in the form of a gasoline or diesel engine. The output shaft of the engine is connected to the cable by means of a geared transmission and a clutch, usually of the automotive type. The transmission output is connected to the cable by an appropriate cable connector. The transmission has a shift lever normally having first, second and third forward positions, and a reverse position. The clutch is actuated by a foot pedal and the engine is provided with a throttle; usually a manual throttle. As a result, the operator of the prior art tool will generally be required to work a manual throttle, a manual gear shift lever and a clutch foot pedal.
In use, the operator will shift the transmission through first, second and third gear to drive the cleaning tool rapidly through the pipe until an obstruction is encountered. At that point, the operator will shift to first or low gear and will adjust for maximum throttle to obtain maximum torque. As a result, the cutting and grinding action is carried out at a relatively low speed of from about 150 to 350 rpm.
An experienced operator can determine, by "feel" and from the appearance of the cable, when he has encountered a particularly difficult obstruction to clear. In particularly difficult instances, the cable may tend to loop or kink. When a difficult obstruction is encountered, the operator will generally depress the clutch and shift the transmission into reverse. It may be that the operator will have to shift between first and reverse many times in order to force the cleaning tool through the obstruction. It will be evident that, in the use of this type of sewer cleaning machine, the operator is substantially constantly manipulating one or more of the throttle, the gear shift and the clutch.
The present invention is based upon the discovery that the prime mover may be used to drive a hydraulic pump. The hydraulic pump, in turn, is used to drive a geared hydraulic motor. The output of the hydraulic motor is connected to the cable through a slip clutch, which serves as a torque limiter. The hydraulic pump is provided with a control valve which controls both direction of flow and amount of flow of the hydraulic fluid, and thus the direction of rotation and the rpm of the hydraulic motor output shaft.
A great many advantages result from this arrangement. First of all, the prime mover or engine runs at constant speed and frequent throttle manipulation is eliminated. The transmission and clutch are also eliminated. Maximum torque is achieved throughout 95% of the rpm range of the hydraulic motor.
The control valve of the hydraulic pump can, itself, be controlled by a lever actuated cable. When the manual control lever is in a central position, the sewer cleaning machine is in an idle mode wherein the pump control valve is set to cause the pump to simply withdraw and return hydraulic fluid to the hydraulic fluid reservoir. As the manual lever is moved forwardly, it will cause the hydraulic motor output, the cable and the cleaning tool to rotate in a forward direction. The rpm rate or speed of rotation will increase, as the lever is pushed forwardly. When the lever is pulled rearwardly from its central position, the elements will rotate in a reverse direction and speed will increase as the lever is pulled rearwardly. Maximum torque is constant above 50 rpm.
The present invention provides full speed control in either direction with maximum torque and maximum cutting ability at any forward or reverse speed above 50 rpm. The sewer cleaner may be shifted between forward and reverse instantly. Finally, both speed and direction can be controlled by the simple manual manipulation of a single lever.